Mila Kunis and Robin Williams boldly plunge into NYC’s East River while filming ‘The Angriest Man in Brooklyn’

Mila Kunis and Robin Williams were really earning their paychecks Tuesday on the set of "The Angriest Man in Brooklyn." Apparently the scene called for the stars to swim in New York City's East River, which has a reputation for being a historically polluted waterway.

While shooting the scene, Kunis, who was outfitted in medical scrubs, was neck deep in the water as she rescued Williams, guiding him to the shore. According to onlookers, the actors did several takes of the scene. Though some precautions were taken: The production team had Kunis dunk her head in a bucket of what appeared to be purified water and sprayed her face with water from the same source, likely so that it appeared that she was completely submerged although she wasn't.

The East River has long been a punch line for jokes about pollution (a memorable episode of "Seinfeld" featured Kramer swimming there with a concerned Jerry noting, "You're swimming in the East River? The most heavily trafficked overly contaminated waterway on the eastern seaboard?"), but it has actually rebounded in the last couple decades. However, an ongoing issue is that the Newtown Creek — which is so massively contaminated that the E.P.A. gave it Superfund status, a designation reserved for the worst contaminated sites in the nation — flows into the East River. Additionally, there are 50 to 60 rainy days each year when New York City sewage water is diverted directly into the East River to prevent it from backing up into people's homes. So while it has gotten better — and continues to — it's not going to be the top pick for where you'll take the family for the beach vacation. And one would think two high-level movie stars wouldn't be that keen on wading into the waters.

Yahoo! Movies reached out to Riverkeeper, which is a watchdog organization dedicated to the protection of the New York waterways (Robert Kennedy Jr. is the chief prosecuting attorney for the group), to find out just how dirty Kunis and Williams' dip was. "The thing about the East River is that it's not really a river, it's a tidal stream connecting the Long Island Sound with the New York Harbor," explained Riverkeeper boat captain John Lipscomb, who was patrolling the East River during our interview. "We are close to the ocean here, so there is a tremendous amount of dilution and extraordinary tidal mixing taking place here, which is actually good for the water."

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Despite the mixing and the proximity to relatively cleaner ocean water, there are still contaminations. Riverkeeper routinely tests the water in the East River and results earlier this month showed about 10 percent of the samples had fecal and sewage contamination. "In other words, if this was a beach, 10 percent of our samples would have caused closure of the beach," explained Lipscomb. "But we've had days here in the East River where after rain, which overloads New York City's sewer systems and causes huge discharges of sewage into the East River, that contamination is four times the federal guidelines." While it rained in New York City as recently as last Saturday — when one of those sewage releases into the East River likely took place — it likely didn't cause high levels. "Given that it wasn't that much rain and two days had passed before these actors were in the water, I can't imagine that fecal contamination was an issue," he said.

So as far as New York City waterways, there are much worse places to film swimming scenes than the East River. "The places where water quality gets really bad in the New York Harbor are the dead ends like Newtown Creek, Gowanus Canal, and Flushing Bay, which don't have the blessing of tidal mixing," said Lipscomb. "They are dead end streets. ... They are just beyond disgusting at times."